Process for finding an additional quantity of fuel to be injected during reinjection in an internal combustion engine

ABSTRACT

A method for determining an additional injected quantity upon reactivation of an internal combustion engine by multiplying a load-dependent wall-film quantity by a correction factor. The correction factor is modulated up during the coasting deactivation time until reactivation with a first time constant. The correction factor is modulated back down during reactivation with a second time constant.

BACKGROUND INFORMATION

German Patent Application No. DE 43 28 835 A1 describes a method thatdetermines an additional injected quantity on a cylinder-selective basisafter reactivation following injection suppression operations forindividual cylinders. Examples of suppression operations includeautomatic slip control (ASR), deactivation while coasting, or an enginespeed or vehicle speed limiter. In this context, the initial value uponreactivation of fuel delivery depends on the number of injections thatwere suppressed to the cylinder in question. After reactivation, theadditional injected quantity is modulated back down to zero, as afunction of the number of injections into the cylinder in question aftersuppression thereof was ended. The additional injected quantity requiredat the time of reactivation is based on a permanently predefinedinjection value that is modulated up with a certain time constant.

It is the object of the present invention to indicate a method fordetermining an additional injected quantity upon reactivation of atleast one suppressed cylinder of an internal combustion engine whichimproves emissions and fuel consumption values as compared to theexisting art.

SUMMARY OF THE INVENTION

The present invention provides a method for determining the additionalinjected quantity by multiplying a load-dependent wall-film quantity,read from a characteristic curve at the time of activation, by acorrection factor. This correction factor is modulated up, during thecoasting deactivation time until reactivation, with a first timeconstant. After reactivation, the previously calculated additionalinjected quantity is modulated back down with a second time constant.

Improved emissions and fuel consumption value result from deriving theadditional injected quantity upon reactivation from a current value forthe wall-film quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figure shows a block diagram for a method for determining anadditional injected quantity upon reactivating of an internal combustionengine.

DETAILED DESCRIPTION

Cylinder-selective injection suppression is usually performed, forexample, with automatic slip control (ASR), during coasting, and in thecase of engine speed or vehicle speed limiting. If rotation speed fallsbelow a minimum threshold, or if the throttle is opened, the transitionoccurs from coasting deactivation (i.e. from injection suppression ofindividual cylinders) to cylinder-selective reactivation. The sequenceof cylinders to be reactivated and their number can be defined by way ofspecific suppression patterns. If the change in throttle valve angle orrotation speed is small, a staged (soft) reactivation occurs; in theevent of large changes in throttle valve angle or rotation speed,reactivation is abrupt (hard). During reactivation, a cylinder-selectiveadditional fuel quantity is required in order to build back up the wallfilm in the air intake duct that was degraded during suppression, whichcan be of different durations for the individual cylinders.

The Figure depicts a block diagram which illustrates how the additionalinjected quantity necessary upon reactivation is determined for acylinder. Block 1 contains a characteristic curve for the load-dependentwall-film quantity in the air intake duct. From this characteristiccurve, the particular present value of the wall-film quantity is readoff as a function of the load signal t1. At node 2, a value WOFF, whichindicates the minimum wall film at idle, is added to the wall-filmquantity WF(k) (ki is a time index) taken from characteristic curve 1.This value WOFF is taken from a characteristic curve 3 dependent onengine speed n, or from a characteristics diagram dependent on enginespeed and engine temperature. This minimum wall-film quantity WOFF can,however, also be taken into account in characteristics diagram 1.

A sample-and-hold circuit in block 4 retains that value of the wall-filmquantity WFM1=WF(k)+WOFF that is present when a reactivation signal B-WEappears at block 4. This sampled wall-film quantity value WFM1S isconveyed to a further node 5, where it is multiplied by a correctionfactor fwe. This correction factor fwe is formed in a block 6. If acoasting deactivation signal B-SA is present, a time constant ZFSA isswitched through via switch 7 to block 6, which forms the correctionfactor fwe. The correction factor fwe is then modulated up, with thetime constant ZFSA, from a minimum value 0 to a maximum value 1. As soonas a reactivation signal B-WE is present, the sample value for thewall-film quantity WFM1S is multiplied by that value of the correctionfactor fwe to which the correction factor in block 6 had been modulatedup at the time of reactivation. The product of this correction factorfwe times the sampled value of the load-dependent wall-film quantityWFM1S then corresponds to the additional injected quantity tewe.

After reactivation, the additional injected quantity tewe justdetermined is modulated back down with a time constant ZFWE.Specifically, as soon as the reactivation signal B-WE is present, switch7 is switched over to this time constant ZFWE, and the factor fwe ismodulated down with the time constant ZFWE. Multiplying thisdown-modulated factor fwe by the wall-film quantity WFM1S sampled at thetime of reactivation causes down-modulation of the additional injectedquantity tewe.

The two time constants ZFSA and ZFWE are defined as a function of theload, the engine speed, or other suitable engine variables.

The additional injected quantity tewe is calculated individually foreach cylinder at the time of reactivation. This is necessary inparticular in the case of staged reactivation, since individualcylinders are then not activated until later, when a different load ispresent. This also results, for each cylinder, in the wall-filmquantities that are modified in accordance with this differing load.

The signal tewe for the additional injected quantity for each individualcylinder is overlaid at a node on a signal te, derived from the loadsignal t1, for the basic injected quantity for each individual cylinder.A correction signal TVUB, which takes into account an energizing delay(which depends on battery voltage) in the injection valves for theindividual cylinders, can also be overlaid at node 9 on the signal tefor the basic injected quantity. It is also advantageous to overlay onthe signal te for the basic injected quantity, at a further node 10, acorrection signal teukg which globally (and not on a cylinder-selectivebasis) takes into account wall-film compensation with rising or fallingload (transition compensation). This global transition compensationsignal teukg is made up of three components, namely a K component, an Lcomponent, and a W component. The K and L components, overlaid on oneanother at node 11, are derived from the change over time in theload-dependent wall-film quantity WF(k). Short-term changes in thewall-film quantity are accumulated as the K component in a first memory12, and long-term changes as the L component in a second memory 13. Thedistinction between the two components depends on the engine speed andthe direction of the load change. The change in wall-film quantity isdetermined with the aid of a delay element 14 which makes available, ata node 15, a value WF(k-1) for the wall-film quantity delayed by onetime unit. Node 15 constitutes the difference between the k-th and the(k-1)-th value of the wall-film quantity, which yields the changes inthe wall-film quantity. The W component of the transition compensationsignal is formed in a third memory 16 which accumulates (for example ona 10-ms cycle) changes in a secondary load signal t1w that depends onthrottle valve position and engine speed. This W component is added tothe K and L components at a node 17.

The transition compensation signal teukg can also be determined in amanner deviating from the method described above.

From the signal te for the basic injected quantity, acted upon by thecorrection signals teukg, tewe, and TVUB, there ultimately results thedesired signal ti for the injected quantity for each individualcylinder.

If a coasting deactivation occurs during a down-modulation of injectedquantity ti, the down-modulation operation is discontinued and thesignal ti is set to zero by means of a switch 18 controlled by thecoasting deactivation signal B-SA.

What is claimed is:
 1. A method for determining an additional quantityof fuel to be injected upon a reactivation of at least one suppressedcylinder of an internal combustion engine, comprising the stepsof:determining a load-dependent wall-film quantity at a time ofactivation; modulating a correction factor, the correction factor beingmodulated up, during a coasting deactivation time until thereactivation, with a first time constant, and being modulated downduring the reactivation with a second time constant; and multiplying theload-dependent wall-film quantity by the correction factor to determinethe additional quantity of fuel.
 2. The method according to claim 1,wherein the first and second time constants are load-dependent.
 3. Themethod according to claim 1, wherein the first and second time constantsare engine speed dependent.
 4. The method according to claim 1, whereinthe additional quantity of fuel is set to a value of 0 if a coastingdeactivation occurs during a downward modulation of the correctionfactor.
 5. The method according to claim 1, wherein the load-dependentwall-film quantity is determined from a characteristic curve.